a) Field of the Invention
The present invention relates to a semiconductor device with an electromagnetic shield, and more particularly, to a leadless package destined for housing a single or a plurality of semiconductor chips or thin film elements which are bare or passivated to a minimum extent or for housing a circuit board on the inner side of which there is surface mounted a plurality of electronic parts.
b) Description of the Prior Art
Among the packages for having mounted therein semiconductor chips such as IC, LSI, etc., plastic packages and ceramic packages have recently been used most widely. Among others, many plastic leadless chip carriers (PLCC) and ceramic chip carriers are used for surface-mounting of such electronic parts. For mounting such plastic molded semiconductor chips on a printed wiring board and using the circuit board as installed in various electronic apparatuses, it is necessary to make an arrangement for preventing the the semiconductor chip from being adversely affected by a noise caused due to an electromagnetic wave produced by adjacent electronic parts, electric circuit or external environment, and also for preventing an electromagnetic wave produced by such semiconductor chip itself from adversely affecting the circuits and electronic parts surrounding the semiconductor chip. To this end, the above-mentioned semiconductor chip used to be covered with a separately formed metallic shield to shield the semiconductor chip against the electromagnetic wave. To provide such a shielding structure for the semiconductor chip, however, an installation space and wiring of grounding conductor are necessary, which causes the packaging density to be lower, installed height of parts to be greater and thus the manufacturing costs to be larger.
A plurality of electronic parts mounted on a printed wiring board used to be electromagnetically shielded by installing to the printed wiring board a shielding case made of a metal having a high electromagnetic shielding performance so as to enclose the electronic parts. Since this is limited in packaging density, compact and lightweight design, however, a shielding structure has been proposed owing to which electronic parts may not always be mounted on the printed wiring board.
For example, the Japanese Unexamined Patent Publication No. 61-166200 discloses a hybrid IC device which has a case formed by a flexible wiring board having a copper foil formed on either side thereof and an insulation layer between these front and rear sides thereof and which is so bent as to enclose electronic parts on the wiring board, the case having mounted on the inner side thereof electronic parts forming a circuit and the outer side being held at ground potential to form an electromagnetic shield. In such hybrid IC device, however, the shielding case formed from the flexible wiring board bent to enclose the electronic parts is inserted in a slot in the printed circuit board and fixed by soldering at the rear side of the printed circuit board. Namely, the electronic parts cannot be mounted on the surface. Also, since the shielding case is formed from a bent flexible wiring board, the shielding case cannot be improved in shape stability and vibration resistance unless a resin is charged in the case after bent.
Also the Japanese Unexamined Utility Model Publication No. 63-149599 discloses a shielding case made of a non-conductive material having a metallic layer formed on either side thereof, the inner side having formed on the metallic layer thereof a circuit pattern on which electronic parts are to be mounted. In this shielding case, the outer metallic layer provides a shielding surface and also a grounding surface. Such as shielding case is mounted on the surface of a printed wiring board. When the circuit pattern formed on the metallic layer on the inner side of the shielding case and the electronic parts on the printed circuit board outside the shielding case are connected as soldered to each other, the higher the packaging density inside the case, the shorter the distance between the connecting terminals connecting the inner and outer sides of the case is (the terminals are to be disposed at a finer pitch). Thus the melted solder will bridge the adjacent connecting terminals, possibly causing a short-circuit.